The present invention relates to a rear suspension system for automobiles and in particular to such a rear suspension system which has a high compliance along the longitudinal direction of the vehicle body or, in other words, in the fore-and-aft direction of the automobile body and yet restricts the change in the toe angle of the wheel as it travels vertically.
The fore-and-aft compliance of a wheel is desired to be high for better capability of the wheel to roll over irregular road surfaces and for improved ride comfort of the automobile, but a high fore-and-aft compliance of a wheel tends to cause an instability in the toe angle of the wheel. The stability of the toe angle is essential for lateral stability of the automobile. As a matter of fact, if the toe angle of the wheel changes as the wheel undergoes a vertical motion the oversteer or understeer tendency of the automobile accordingly changes and this is disadvantageous in terms of the handling of the automobile. A high fore-and-aft compliance of a wheel may also cause an instability in the camber angle of the wheel and it should be likewise controlled. The ability of the wheel to resist the changes in the toe angle and the camber angle are referred to, hereinafter, as the toe angle rigidity and the camber angle rigidity, respectively. Thus, not only the toe angle rigidity of the wheel but also the camber angle rigidity of the wheel are desired to be as high as possible.
Rear suspension systems for automobiles using a trailing arm and three lateral links are disclosed, for instance, in Japanese patent laid-open publication Nos. 60-53408 and DE-OS 2038880. The suspension system of this type offers much freedom in various design parameters and permits a good control of the toe angle and the camber angle by appropriately arranging the lateral links and determining their lengths. However, these conventional rear suspension systems do not necessarily offer a high compliance of the wheel along the fore-and-aft direction. Furthermore, a shock absorber element including at least a damper or a spring is required to be connected to an upper arm or the knuckle itself which supports the wheel and the compactness of the suspension system is impaired with the shock absorber element extending above the suspension system into the space for a passenger compartment or a trunk. This is due to the fact that there is no lower arm which is located exactly below the axle to connect the lower end of the shock absorber element.